1. Field of the Invention
The present invention generally relates to an electronic still camera and, more particularly, to an electronic still camera for recording an electronically photographed still image in a predetermined recording medium such as a memory card upon data compression.
2. Description of the Related Art
With an improvement in performance of solid-state image pick-up elements such as a charge-coupled device (CCD), various electronic still cameras using solidstate image pick-up elements have recently been developed. An electronic still camera of this type is designed such that an electronic still image, which is electronically photographed by a CCD or the like, is recorded in a recording medium such as a floppy disk or a semiconductor memory card, and the recorded image signal is read out to be reproduced by a TV receiver or the like.
According to such an electronic still camera, unlike a conventional camera using a silver chloride film, a photographed image can be instantaneously monitored without film development and printing. Another advantage of this electronic still camera is that a still image signal can be directly transmitted through a data communication line.
Generally, in an electronic still camera using a floppy disk as a recording medium, about 50 recording tracks are concentrically formed on the floppy disk, and one electronic still image is recorded in each recording track.
An electronic still camera of this type, however, is designed to dynamically record electronic still images by means of a floppy disk driving mechanism. Therefore, problems are posed in terms of cost performance.
Under the circumstances, various attempts have recently been made to develop electronic still cameras using large-capacity memory cards which have been put into practical use with advances in semiconductor technology.
An electronic still camera using such a memory card as a recording medium is designed to sequentially record electronic still images in accordance with address control with respect to the image memory. This camera is advantageous in that still image signals can be statically recorded and read out at high speed.
That is, when a memory card of this type is used as a recording medium, still image signals can be recorded by only performing address control with respect to the image memory. Therefore, it is required for such a camera to record a large number of electronic still images by efficiently using the limited storage capacity of a memory card.
For this purpose, a method based on data compression has been studied. In this method, electronic still image data is compressed by variable-length encoding data compression such as an adaptive differential pulse code modulation (ADPCM) or an adaptive discreate cosine transform (ADCT) in accordance with the contents of the data, and the encoded compressed data is recorded in a memory card. According to such variable-length data compression encoding, since image data can be compressed in accordance with the contents of an image so as to be reduced in amount, a large number of electronic still images can be recorded in a memory card while the memory area on the memory card required to record one electronic still image is reduced.
When electronic still image data are to be recorded in a memory card upon data compression by variable-length encoding data compression, the data amount of each electronic still image to be subjected to data compression is determined in accordance with the contents of each image. Therefore, a user cannot know a proportion of the memory area in the memory card which already records electronic still images. In other words, a user cannot know an empty area in the memory card and the number of electronic still images to be photographed which can be further recorded.
Published Unexamined Japanese Patent Application No. 1-185080 discloses a technique providing an improvement with regard to this point. In this technique, whether a last photographing operation can be performed or not is determined by comparing the data amount of a scene to be photographed with the remaining storage capacity of the memory. If the last photographing operation cannot be performed, an alarm is generated.
In such a conventional technique, however, an alarm is generated only when it is determined that a last photographing operation cannot be performed. Therefore, during the photographing operations, a user cannot know in advance how many more electronic still images can be recorded.